How to Spot and Fix a Watch Battery Leak

The electrolyte used in a Silver Oxide watch battery is highly alkaline and corrosive and so when a battery leaks inside a watch it can be catastrophic for the movement.

In a combined survey of over 3000 watches where the battery had expired, the percentage of those expended batteries that had leaked was more than 40%. (The full conclusions of the survey are towards the end of this article).

Of those leaked batteries, a third, or between 12-15% of the total number of watches examined, were sufficiently damaged to warrant either a full-service or total replacement of the watch movement.

In the remaining two thirds of the cases where the battery had leaked, the damage done was not severe enough to warrant a service of the watch or an exchange of movement, but rather a simple clean-up, which will be demonstrated later.

As you can see, this under-reported problem can be the cause of great expense and inconvenience to the owner of a quartz watch. There are however certain steps you can take to limit your exposure to any potential problems, which this article hopes to introduce.

You can clearly see the damage done to the movement of the watch once the leaked battery has been removed. The plastic isolator has been badly spoiled, and there are significant amounts of crystallised residue left which will further contaminate the watch. Most of the damage is beneath the brass cover however. The battery leak will have travelled along the negative contact and reached the integrated circuit. Even a small amount of corrosion on the circuit will render it useless, and in cases such as this it is not economically viable to service or repair the movement; instead it will need to be replaced

To learn why Silver Oxide batteries leak so frequently, it is important to understand how the battery is assembled.

The watch battery is split into two distinct parts, the anode can (negative) and the cathode can (positive). The anode is a gel containing a mixture of the negative electrode (Silver Oxide) and the electrolyte (Sodium Hydroxide). The cathode contains the positive electrode (Zinc). Each part is surrounded by a metal shell, coloured grey in the above image, which forms the outside of the cell as well as acting as the corresponding positive and negative contact points.

A separator, which is usually a mesh, prevents the electrodes from mixing but allows ions to flow between each half of the cell.

Although the electrodes do not touch one another, they are electrically connected by the electrolyte.

The insulator ensures that the two parts of the casing are held in place and do not touch one another. It also acts as a seal preventing the chemical mixtures from escaping. It is usually made from nylon. Sometimes it is referred to as the gasket.

As a battery cell ages the separator can degrade, this can allow some of the electrolyte in the anode to come into direct contact with the zinc in the cathode. When this happens electrolysis occurs.

Because electrolysis only occurs once the separator has degraded, the possibility of a battery leaking increases as the battery approaches its shelf life expiry. Other factors such as temperature and remaining capacity also contribute to the likelihood of the electrolyte escaping.

Electrolysis is a chemical reaction where the sodium hydroxide electrolyte splits and passes its oxygen onto the zinc.

In the below formula Na is Sodium, O is Oxygen, H is Hydrogen and Zn is Zinc.

Hydrogen is the least dense element, in fact once separated from the electrolyte it takes up over 20 times more volume inside the battery case. As the cell is sealed the hydrogen cannot escape which causes a build up of pressure.

This pressure, as it tries to equalise itself with the outside air, will try and push its way out. As we can see from the diagram above, the insulator (coloured red) is the weak point, and this is where the gas will try and escape through. If the build up is significant enough, the insulator will rupture allowing the hydrogen gas to escape.

Once this seal is broken, the highly alkaline and corrosive electrolyte is then free to leak out of the battery. Any additional Hydrogen gas being produced will help to expel the electrolyte at a faster rate.

If you look across the top of this battery you will notice that it is raised slightly. This is due to the pressure volume inside the cell increasing due to the release of hydrogen gas, which has caused the metal casing to buckle. This shows that electrolysis has already occurred inside the battery, but that the hydrogen gas has not yet been able to escape and this battery has not yet leaked. This cell must be immediately replaced.

Mercury Content in Silver Oxide Cells

A battery displaying that it has no Mercury content (Hg 0%). Previously Mercury comprised around 0.2% of the internal chemistry of a battery. Its purpose was to inhibit the electrolysis and help prevent a battery from leaking. Environmental and health concerns with the use of Mercury however led in 2004 to Sony producing the first Silver Oxide cells with no Mercury added. Currently 0% Mercury Silver Oxide cells are the most widely used

Electrolytes

There are two types of electrolyte used in Silver Oxide watch batteries. We have already discussed Sodium Hydroxide, which is the most common type, and is in use in the general low drain batteries for standard quartz watches.

Sodium Hydroxide can also be known as either Caustic Soda or Lye

In what are termed high drain batteries, Potassium Hydroxide (KOH) is used.

Potassium Hydroxide is sometimes called Caustic Potash or Potash Lye

The function of the electrolytes is almost identical in both low and high drain batteries, however in a low drain cell the internal resistance is higher, which limits the amount of energy that can be drained at any one time. High drain cells have a much lower internal resistance, which means that if a watch demands a large amount of energy, such as for sounding an alarm, then the battery will provide it.

Both electrolytes have a similar white crystalline appearance, have a comparable corrosive nature and both are used in the form of a slightly liquid gel which helps aid their conductivity. The fact that it is a liquid is what allows the electrolyte to flow and therefore leak.

In high drain batteries the separator is thinner, which allows the cell to provide larger pulses of energy if required. The downside to this is that it is more susceptible to degrade.

As a result: high drain batteries are significantly more likely to leak than low drain cells.

Crystals of Sodium Hydroxide (NaOH). Caustic acid or lye, as it is otherwise known, has been in use for around 5000 years as an ingredient in soap

Safety Notice: care should be taken when touching a leaked battery, or any chemical residue, as both types of electrolyte will decompose proteins and lipids in the skin. These chemicals have a strong exothermic reaction as they dissolve in water; the heat from which can cause a chemical burn. Latex gloves or finger cots are therefore recommended when handling expended batteries. If your skin does come into direct contact with any leak from a battery you should dry brush any trace of chemical from your skin before you attempt to wash the area with water

Lithium Watch Batteries

A 3V Lithium coin cell. The Lithium range of batteries use a very different chemistry to Silver Oxide cells and have no risk of leaking due to electrolysis

Identifying Watch battery leaks

In some cases the battery leak is so severe that you do no need to remove the cell from the movement to identify the problem. In this example the corrosion is speckled on the surface of the watch movement. This is not a natural corrosive pattern and would indicate that someone has already removed the battery, noticed the leak and replaced it back – splashing the leaked electrolyte as they did so

Although less obvious than the previous example, there are also clear signs of a battery leak in this image. Firstly, rather than being a mirrored silver finish, the top of the battery is tarnished. Above the battery is the negative testing point. This should a golden brass colour, but, like the battery, it is badly discoloured. Another very subtle hint is in the same area; if you look closely you can see that the corner of blue circuit board is not completely flush. When a battery leaks, the corrosion often travels along the negative contact on the underside of the battery. This leads to the part of the circuit where the negative testing point is and any corrosion underneath will warp the circuit board causing the very slight curling we can see

In some cases you can find evidence that the battery may have leaked without the need to open the watch. On occasion the leaked battery fluid will travel through the circuit, onto the wheels of the gear train and finish at the hands of the watch. Here the electrolyte has reached the hands and crystallised

Another example of damaged hands caused by a possible battery leak. It is important to note the difference in the appearance in the corrosion when compared to a watch that has had moisture enter it. Water damage will cause a dulling of the metal with possible signs of rust. Any other metal parts, such as the batons on the dial, will usually be affected too. In the case of a battery leak, the damage is confined to small clusters, often leaving a white residue. It is rare for the dial to be damaged. This is because the electrolyte remains a liquid until it solidifies, whereas water can repeatedly change from a vapour to a liquid and back allowing the corrosion to be more widespread

It is straightforward to see if a battery has leaked if you look at the underside around the insulator. Here the electrolyte has returned from a gel into its natural crystallised form. These crystals are very brittle and will crumble if touched. Even if a leak has not caused damage to a watch movement, these crystals can form debris in a watch that like dust, hair or dirt will require the movement to be serviced to remove

A typical indicator of a battery that has just started to leak is shown here by the curved patch of moisture on the battery isolator. This “moisture” is actually the electrolyte as a gel which has not yet crystallised. While in this relatively contained form, the leak can be cleaned off using a product such as Rodico. For the most part you can overcome the need to fully service the watch by cleaning or replacing the isolator

In this example the battery has also just started to leak, however you will note that in this case the negative battery contact has some tarnishing on it. As the battery contacts are an integrated part of the circuit board if this is not just some grease or dirt that can be cleaned off, but rather corrosion caused by a battery leak; then the entire circuit board needs to be replaced and this watch will need servicing

In this example from a quartz chronograph movement the battery leak is very severe. This watch will need servicing and it likely that many of the components will be unsalvageable

This particular battery has leaked very badly. An example of poor practice here is that the previous watch technician has signed the battery (this is done so that they will recognise their work the next time they see the watch). Rather than writing with a soft felt pen on the top side of the battery or the inside of the case-back, they have instead used a metal scriber to scratch both their initials and the date of their work on the underside of the battery. It is entirely possible that the pressure added to the battery while this was being etched weakened the seal enough to later cause the battery to leak so drastically

The corroded steel case of the cell bears testament to the potent nature of the battery’s alkaline chemistry

How to Clean a Watch Battery Leak

In cases such as above, where the battery leak is not severe enough to warrant a service of the movement, if we are careful we can completely remove the leaked chemicals and prevent any long-lasting damage to the watch

Take a clean piece of a product such as Rodico and make the tip into a point. With the end make a quick dab onto the spoiled area. You should then fold the tip back into the rest of the material and form a new point. Continue to dab at the leak, folding the point back and remaking it after each attempt. Do not make a wiping motion as this will spread the leak, and always remember to keep the tip clean and fresh by reforming it each time

You should be able to remove all of the electrolyte and leave the watch in a condition where it would be unapparent that there had ever been a leak. Always throw away the Rodico you have cleaned the area with

Survey Results

A combined survey was undertaken to assess the issue of watch battery leaks. The outcome of the survey comes from the evaluation of over 3000 watches where the battery had expired. The results derive from a mix of sources from both North America and Europe including independent watch repair centres, official branded workshops and solo enterprises. The variety of watches tested covers the full-range of prices and brands that occupy the majority of the market segments.

In these results the use of the phrases such as “Best” or “Better than” relates only to the cell’s relative potential to leak, and should not be taken as a recommendation of which type or brand of cell to use. When selecting a battery the overall characteristics must be considered. Quality indicating factors such as the relative flatness of the discharge rate over the cell’s lifespan, or the total capacity of the battery, were not examined.

The conclusions will be presented as a comparison to the parts considered. This is because although there was some variance in the results based mainly on geographical area, the results were all in agreement when viewed in the form of a general list as exhibited below.

Many thanks to those individuals and businesses that participated in this survey.

As discussed earlier, the need for the separator to be thinner in a high drain battery is one of the major contributory factors that lead this battery type to leak more frequently than a low drain cell.

The height of the cell appears to be the main contributory factor in the likelihood of a battery leaking.

Examples; Wide and Tall 394/SR936SW, Wide and Short 371/SR920SW

Taken in isolation these results can be misleading. However when you note that most quartz Chronograph watches use Wide and Tall cells and quartz Gents movements generally use Wide and Short battery sizes ,the relationship between the type of movement and the chance of a leak occurring is more apparent

Only brands where more than 100 examples of drained batteries were examined are included. “Origin” was noted due to the clustering of results that became evident. This could be due to the regional exchange of technology and resources where the cells are manufactured. The difference in each of the “Rating” is based on the derived rate for the likelihood of a battery leaking, and are separated by a difference in the potential leaking rate of at least 3%.

Although not included in the results, unbranded batteries if grouped together were by far the most likely type to leak.

Energiser now only produce their button cell range in “Multi-Drain”. In the above example the cell is named as both the low drain 395 (SR927SW) and also the high drain 399 (SR927PW), and Energiser claim that this cell is a direct replacement for either type; able to deliver both a constant low drain and a pulse of high drain current if required. In the survey these batteries were grouped together with either high or low drain cells based on the type they were replacing

Rayovac and Varta are part of Spectrum Brands Inc. The examples above show Rayovac batteries made in USA, Swizterland, Germany and Japan. This strongly hints that these companies are rebranding 3rd party batteries

How to Reduce the Risk of your Watch Battery Leaking

You will never be able to completely exclude the risk of a Silver Oxide battery leaking. The following tips however can be followed to reduce the risk of the watch needing a full-service or exchange of movement:

Do not leave a battery in a watch unless you intend to use it

Do not wait until a battery has died before replacing it

When fitting a battery, if possible use one that is less than 6 months old

Any stocks of watch batteries should be refreshed every year

Always use a branded battery

Always remember to recycle your old Silver Oxide button cells – even leaked ones. Not only does it stop harmful chemicals contaminating the environment, but the cells retain some value and so can be sold for scrap to an appropriate recycling company.

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8 Responses

I purchased and expensive Omega watch and didn’t wear it. Two years later when I wanted to wear it had stopped. I took it in to have a new battery fitted, the shop sent it back to Omega who now say I need replacement works as the battery has leaked. Charge £320!!!

I had no idea this could happen until today. Buyers should be warned about possible leaky batteries.

I once had watch I bought on the beach in Thailand for £3 it lasted for ten years. I only replaced the battery once.

I have a Seiko watch with has taken up stopping when I fly long haul routes in Asia. This is the second episode it has done it and the battery this time can be seen to leak. Sometimes returning to the ground it will start again but once it starts stopping you need a new battery. Has anyone else seen this?

Thanks for your comment. If your watch is experiencing a change during a long flight, then it’s likely caused by the change of air pressure. This means two things:

Firstly, your watch is not sealed properly. Most watches should have some degree of water resistancy, but this ability relies upon rubber seals which degrade and perish over time.

Secondly, your watch battery was already leaking before your flight. The change in air pressure on a normal aeroplane will not be anywhere near significant enough to cause a battery to leak. However it will accelerate any leak that is already occuring.

So my advice would be to get your watch resealed, change the battery and have any leak cleaned; and remember to change your watch battery after 2-3 years.

You don’t wait for your car to breakdown before you get it serviced afterall 🙂

Thank you very much indeed, Colin, for such a thorough, well written and illustrated piece on this matter.
If I may, I’d like to ask following image 9 starting from top: if small green specs on the negative testing point can be observed, will Rodico remove them or is it clear indicator that corrosion is underway along the entire negative contact underneath the blue circuit board and thus needs to be entirely replaced? In other words, once corrosion has begun on metal parts, what can be done?
Thank you in advance for your kind reply.

Thank you for your comment. Once corrosion has started there is not a great deal that can be done. It is not always an immediately fatal fault though, and so the watch can still work even after a battery has leaked and corrosion has started. If the leak is cleaned up properly, with peg wood and Rodico, it can stem the further increase of damage, however it is not something that can be repaired; and so as you mentioned, the circuit plus any other affected parts would need replacing when the watch eventually fails. Colin

Interesting read, I have mostly mechanical watches but do have 2 basic quartz watches that my dad “forgot” to return when he left the armed forces. They both use eta 955.102 movements, I’ve always used Renata batteries (since they’re made by the same folks that make the movt) but I think now I’ll be switching to energiser to minimise the risk of leaks.

Although Swatch own both Renata and ETA, they both operate very independently from one another and so there aren’t any quality links between the two companies.

Renata is the industry standard, and almost every major watch brand uses them, although I’ve been suprised since publishing the article how many other watchmakers have told me that they always had a suspicion about the quality of Renata batteries. I’ve no interest in promoting one brand over another, but Energiser does seem to be a more stable choice. The 955.102 movement is now obsolete and so if you’re wanting to keep the original movement in the watch for as long as possible, then choosing a good battery will go a long way.